Groundwater

• Review- Things to Know

  -Recognize how much groundwater is on Earth

  -Porosity & permeability

  -Aquifer types

  -Consequences of overdrafting

  -The Love Canal crisis
• Hydrologic Cycle


  -Ocean are the biggest source of water

  -Glacial ice is the second biggest source

  -Groundwater is the third biggest source
• Runoff


  Water that moves across the land surface and into streams and rivers
• Infiltration


  Flow of water from the land surface into the subsurface.

  -becomes groundwater
• Infiltration Properties


  Two key properties to measure
• #1 Porosity- measurement of how much open void space there is in the area (percentage); space that can be filled in with water


  a- Intergranular pores: little tiny opening between the grains (blue color on the images)

  -Small but when added together it can be a lot of area for stored water

  -The most important

  b- Fractures: fractures within the rocks that can become a natural pathway for water to flow through and start to fill up

  -Have to be in an area with highly fractured rocks

  -Not very common

  c- Vugs (vuggy)- dissolved material to leave pore space behind that can be filled with water

  -Includes caves and caverns
• Controls on Porosity


  Determined by sediment/rock properties:

  -Sorting

  --Well sorted, high porosity

  --Poorly sorted, low porosity

  -Cementation

  --Well cemented, low porosity

  --Poorly cemented, high porosity
• #2 Permeability- can the water flow through the material; how easy is it for the material to flow through that substance


  -Connected pores give a rock permeability
• Water Table (WT)


  boundary below ground that separates the saturated zone (phreatic zone) below it from the unsaturated zone (vadose zone or zone of aeration) above it
• Aquifer


  any layer of material that can provide us with a usable layer of water

  -Recover for human use via wells
• Types of Aquifers


  -Unconfined- aquifer sits on top of an impermeable aquitard

  --Aquitard- very low permeability; not going to let any water get any deeper

  -Confined- aquifer is stuck between two aquitards; impermeable layer below and above; water cannot fill up as fast
• Artesian well


  natural water pressure will pump the water up for you; no need for expensive mechanical pumps to pull the water up rather you just have to drill a hole in the correct spot at the base of the slope where the pressure is high

  -Used for confined aquifers
• Water Supply


  -Recharge- all water you are putting into the aquifer (infiltration and water naturally flowing in)

  -Discharge- all water you are taking out of the aquifer (pumping out and water naturally flowing out)

  --Want recharge = discharge: If unbalanced there are issues
• If Recharge > Discharge, water table rises

  Construction problems
• If Recharge < Discharge, you're overdrafting


  overdrafting: water is getting less and less over time
• Effects of overdrafting


  1 - cone of depression

  2 - subsidence

  3 - salinity contamination
• Cone of Depression


  -around the well that is pumping two fast you start to see a cone (upside down) that keeps getting depressed

  -Becomes a problem when the tip of the cone is below the well so you just pump air

  -Fix it by slowing down the pump
• Subsidence


  A depression of the land surface as a result of groundwater being pumped. Cracks and fissures can appear in the land. Subsidence is virtually an irreversible process.

  EX: Subsidence in California
• salinity contamination


  Desalinization- taking salt water, running it through filters, and extracting the salt to make it into fresh water

  -Possible just expensive
• GW Movement


  Typically GW moves very slow

  -Good: cannot rapidly drain; once you find it is going to be there long term

  -Bad: if water becomes contaminated it takes a long time for that contaminated body of water to flow away
• Erodes even at slow speeds

  Groundwater carries dissolved substances

  -CO2 and SO2 dissolve

  -carbonate rocks

  -Ex: sinkholes
• Case Study: Groundwater Contamination

  Love Canal, Niagra Falls NY
• Early 1900s


  people were trying to build canals along the rivers but they never were put to use
• 1940s


  old canals became chemical waste dumps by a local chemical company where generated chemicals for WWII
• 1960s


  -many people moved there and put a strain on the real estate market

  -Chemical company was reluctant to sell the dump sites but sold it for $1

  -Local government opened it up for building which meant it had to be dug into which removed the sediments that kept the chemical sediment in place

  -Recharge was getting higher and closer to surface bring old contaminants with it contaminating the aquifer
• 1970s


  people began to notice health issues in the community
• 1978


  ocal homeowners learn there's 21,000 tons of chemical waste underground

  -Who's responsible?
• Aug 7 1978


  president Carter declared a declaration of emergency to evacuate neighborhoods
• 1980


  'Superfund Act': piece of legislation that cleared the way for federal government to step in and help

  -effects still appeared in 1994
• Love Canal Aftermath


  2008: survey of 4 states found 500,000 kids in schools < ½ mile from waste dumps, including one on top of a PCB dump